AIDS (acquired immunodeficiency syndrome) was first discovered in San Francisco in 1981 as a fatal immunodeficiency disease of homosexual males (Gottlieb, M. S., Schroff, R., et al., N. Engl. J. Med., 305, 1425-1430(1981)). Two years later, the Montanie group of the Pasteur Institute in France discovered the virus that causes AIDS (Barre-Sinoussi, F., Chermann, J. C., et al., Science, 220, 868-871(1983)). In 1985, this virus was univocally named HIV (human immunodeficiency virus) (Coffin, J., Haase, A., et al., Science, 232, 697(1986)).
AIDS is a disease having the following features and effects: When an individual is infected with HIV through sexual intercourse, blood transfusion, etc., the virus destroys the immunological functions of the infected individual, causing acquired immunodeficiency of the host, i.e., the infected individual. Eventually, the host manifests a variety of symptoms such as diarrhea and pneumonia, resulting in a final outcome of death of the host.
Presently, many researchers are attempting to develop remedies for AIDS. For example, since the discovery of azidothymidine (AZT) by Mitsuya et al. (Mitsuya, H., et al., Proc. Natl. Acad. Sci., USA., 82, 7096(1985)), ddI (2',3'dideoxyinosine), ddC (2',3'-dideoxycytidin), and other substances have been studied in clinical situations. However, pharmaceuticals providing satisfactory results have not yet been reached.
Although the incubation period from infection with HIV to onset of disease greatly varies depending on the individual, about 50% of humans who are infested with HIV manifest the disease with certainty within 10 years after infection, and almost all the infected patients die within 1 to 3 years after manifestation of the disease. Adults over 40 years of age and children rapidly develop the disease after they are infected with HIV. Reasons that explain the grace period between infection and development of AIDS-related complex (ARC) may include the patients' general health conditions, genetic predisposition, complications with other infection disease, and other host-dependent causes, as well as differences in the strain of infectious virus.
In cases of infection due to transfusion of blood components, most HIV-infected individuals manifest AIDS and die. However, some infected individuals do not manifest AIDS even after 10 years have passed after infection, and some other infected individuals take an even longer time before manifestation of AIDS. Such cases are seen worldwide, and it has been reported that 5% of HIV-infected individuals survive for long periods. So-called long-time survivors among HIV-infected persons, who stay asymptomatic for long periods, have received much attention, because they are considered to offer a clue for elucidation of the mechanism of their resistance to HIV virus or preventing the manifestation of the pathological symptoms. Therefore, a variety of studies and research have been performed on such long-time survivors.
However, the reason why longtime survivors do not manifest AIDS in spite of having been infected with HIV has not yet been clearly understood. Thus, it is desired to clarify the reason of HIV resistance, and to develop remedies for treating HIV diseases on the basis of the reason.